1. Field of the Invention
The disclosures herein relate to a cooling device used in a printer, a facsimile machine, a copy machine or the like, and an image forming apparatus provided with the cooling device.
2. Description of the Related Art
As an image forming apparatus, one type of image forming apparatus is known in which an electrophotographic technology is used for forming a toner image on a recording material. The toner image on the recording material is applied with heat and pressure to fix the toner by a fixing device. If the heated recording material after fixation is stacked in a sheet ejection tray, heat accumulated in a bundle of recording materials may soften the toner. If more recording materials are stacked on the bundle of recording materials with the softened toner, pressure is generated by the weight of the bundle of recording material. The pressure may cause a phenomenon called a “blocking” in which the recording materials are adhered to each other by the softened toner. Once a blocking occurs, toner images on the recording materials may be deamaged if the recording materials are separated forcibly.
To prevent a blocking from occurring, a cooling device is needed which can sufficiently cool down a recording material soon after fixation by heating. A cooling device for a recording material is already known that uses a cooling member, in which liquid coolant or refrigerant is circulated, to make contact directly/indirectly with a conveyed recording material to absorb heat from the recording material. For example, Japanese Laid-open Patent Application No. 2006-258953 discloses a cooling device including a cooling member in which a circulation passage of liquid coolant is provided to cool a cooling surface of the cooling member. The cooling surface is made to indirectly contact with a recording material via an endless belt. The circulation passage in the cooling member has multiple passage sections arranged in the direction perpendicular to the recording material conveying direction, and folded passage sections to connect adjacent passage sections to guide liquid coolant from an upstream passage section to a downstream passage section so that the liquid coolant can change its flowing direction around edges of the cooling member.
However, such a cooling device as disclosed in Japanese Laid-open Patent Application No. 2006-258953 may cause a defect due to its configuration that has folded passage sections of the circulation passage inside of the cooling member, as follows. The more the number of folded passage sections of the circulation passage for liquid coolant are, the stronger the cooling effect at the edges of the cooling surface of the cooling member (the edges in the direction perpendicular to the recording material conveying direction, or vicinities of the folded passage sections) becomes than the other parts of the cooling surface. This is mainly because a heat exchange area for liquid coolant contacting the inner surface of the circulation passage is larger at vicinities of the folded passage sections than at the multiple passage sections, in terms of per unit width in the direction perpendicular to the recording material conveying direction. This causes a problem with image quality such as gloss of a recording material has unevenness between the edges and the center.